1. Field of the Invention
The present invention relates to a radio system and a radio communication method, and more particularly to a radio system and a radio communication method which transmit and receive a radio signal between a mobile station and a donor base station and/or a relay base station.
2. Background Art
In recent years, a service area of cellular phones is enlarged, and there are a large number of operators that exceed 99% in population coverage in Japan.
However, a status of indoor area maintenances such as underground cities or tall buildings will be still insufficient.
Because the indoor area maintenance is technically difficult, and expensive, in fact, the area maintenance is difficult.
The indoor population coverage largely falls below the above population coverage.
On the other hand, according to data, a frequency at which users use the cellular phones indoor exceeds 70% of the total, and complaints from the users have a higher proportion of contents related to the indoor service area.
At present, as one of indoor area maintenance countermeasures, there is a femto base station.
The femto base station is an ultraminiature base station that can be installed inside homes or offices, and features of the femto base station reside in that the output is low, the capacity is low, and the price is low. This femto base station is rapidly popularized domestically and internationally.
Another feature of the femto base station resides in that an internet can be connected as a backhaul.
A femto base station of long term evolution (LTE) is disclosed in 3GPP TS36.104 V9.4.0 (pages 16 to 19).
The femto base station of the LTE is called “home evolution node B (HeNB) or home base station (HomeBS) in a 3GPP.
The femto base station can be connected to the internet, and therefore has such an advantage that the femto base station can be easily installed within homes or offices.
On the other hand, as a base station proposed to facilitate the installation of the base station as a first purpose, there is a relay base station.
The details of the relay base station are disclosed in 3GPP TS36.300 V10.0.0 (pages 25 to 30) and 3GPP TR36.912 V9.3.0 (pages 17 to 20).
FIG. 1 is a diagram illustrating a configuration of a relay radio system according to a conventional example.
Hereinafter, an outline of the relay radio system using the 3GPP will be described with reference to the drawings.
In the 3GPP, the relay radio system is classified into a TYPE 1 and a TYPE 2, and in this example, a mode using an inband in the TYPE 1 will be described.
The relay radio system of the 3GPP includes a donor base station 501, a donor cell 502, a mobile station 503, a relay base station 504, a relay cell 505, a mobile station 506, and a core network 507.
The donor base station 501 forms the donor cell 502, and the relay base station 504 forms the relay cell 505.
The conventional relay base station 504 is frequently located within a communication area of the donor cell 502 formed by the donor base station 501, and particularly arranged at a cell edge of the donor cell 502.
It is assumed that the mobile station 503 is located within the communication area of the donor cell 502 formed by the donor base station 501, and the mobile station 506 is located in the relay cell 505 formed by the relay base station 504.
It is assumed that the donor base station 501 communicates with the mobile station 503 and the relay base station 504, and the relay base station 504 communicates with the mobile station 506.
The donor base station 501 is connected to the core network 507 with the aid of a backhaul connection of an operator dedicated line by wire.
The relay base station 504 has a function of transferring data of control (C)-plane and user (U)-plane communicated between the core network 507 and the mobile station 506 through the donor base station 501 by a radio link.
The data of C-plane communicated between the core network 507 and the mobile station 506 means control data such as transmission or reception.
The data of U-plane communicated between the core network 507 and the mobile station 506 means real user data.
Data transfer between the donor base station 501 and the relay base station 504 is conducted by using a given specific sub-frame.
FIG. 2 is a diagram illustrating an appearance of the data transfer in the conventional example. FIG. 2 illustrates the appearance of the data transfer among the donor base station 501, the relay base station 504, and the mobile station 506.
The donor base station 501 receives downlink data of the C-plane and the U-plane transmitted from the core network 507 through a backhaul connection 508, and subjects the downlink data to signal processing of each layer to obtain a downlink transmission signal Down Link (DL)-TXd.
The donor base station 501 transmits the downlink transmission signal DL-TXd with the aid of a multicast broadcast over single-frequency network (MBSFN) sub-frame.
In the present specification, the sub-frame means a data interval having a given period, for example, 1 [ms], and the MBSFN sub-frame means each specific sub-frame which is inserted into a given number of sub-frame intervals, for example, 10 sub-frames.
FIG. 2 illustrates a case in which one MBSFN sub-frame is inserted at 10 sub-frame intervals.
The MBSFN sub-frame is used for the purpose of being originally used in an MBSFN service of an LTE, but can be used for the purpose of transferring data between the donor base station and the relay base station.
A multicast (including broadcast) sub-frame may be used instead of the MBSFN sub-frame.
Also, the donor base station 501 communicates the mobile station 503 existing within the subject cell with the aid of a sub-frame other than the MBSFN sub-frame. One mobile station may use all or plural sub-frames, or the plural mobile stations may share the plural sub-frames.
The relay base station 504 receives the transmission signal DL-TXd transmitted from the donor base station 501 to obtain a downlink reception signal DL-RXr.
The relay base station 504 subjects the downlink reception signal DL-RXr to signal processing of each layer in the base station to obtain a downlink transmission signal DL-TXr.
The relay base station 504 transmits the downlink transmission signal DL-TXr toward the respective mobile stations 506 existing within the cell of the relay base station 504 by the aid of the sub-frames other than the MBSFN sub-frame.
Each mobile station 506 receives the downlink transmission signal DL-TXr transmitted from a relay femto base station to obtain a downlink reception signal DL-RXu.
On the other hand, each mobile station 506 transmits an uplink transmission signal up link (UL)-TXu of the C-plane and the U-plane with the aid of the sub-frames other than the MBSFN sub-frame.
The relay base station 504 receives the transmission signal UL-TXu transmitted from each mobile station 506, and subjects an uplink reception signal UL-RXr to signal processing of each layer in the base station to obtain an uplink transmission signal UL-TXr.
The relay base station 504 transmits the uplink transmission signal UL-TXr with the aid of the MBSFN sub-frame.
The donor base station 501 receives the transmission signal UL-TXr transmitted from the relay base station 504 to obtain an uplink reception signal UL-RXd.
The donor base station 501 subjects the uplink reception signal UL-RXd to signal processing of each layer in the base station to obtain uplink data of the C-plane and the U-plane.
The donor base station 501 transmits the uplink data of the C-plane and the U-plane to the core network 507 with the aid of the backhaul connection 508.